MICHIGAN’S SAND DUNES Geological Survey Division Pamplet 7 By Steven E. Wilson Lansing, Michigan Copyright © 2001 by the Michigan Department of Environmental Quality (DEQ) Geological Survey Division (GSD). The DEQ GSD grants permission to publish or reproduce this document, all or in part, for non-profit purposes. The contents of this electronic document (whole or in part) can be used if, and only if, additional fees are not associated with the use or distribution of this document and credit is given to the DEQ GSD and the author(s). This copyright statement must appear in any and all electronic or print documents using this file or any part thereof. Geological Survey Division character it is the subject of many in-depth technical reports. This pamphlet is designed to introduce Pamplet 7 Michigan's Sand Dunes to you. AN MICHIGAN’S STUDY OF COASTAL SAND DUNE MINING IN MICHIGAN WHAT IS SAND? By Steven E. Wilson Lansing, Michigan, 1979, 2000 Before we try to describe a sand dune, we need to know what sand is. This question does not have a Copyright © 2001 by the Michigan Department of Environmental simple answer. The designation "sand" does not refer Quality (DEQ) Geological Survey Division (GSD). The DEQ GSD grants permission to publish or reproduce this document, all or in to how the material was formed or what it is made of. part, for non-profit purposes. The contents of this electronic Sand can, and does, come from all three major rock document (whole or in part) can be used if, and only if, additional types: igneous, metamorphic, and sedimentary. Sand fees are not associated with the use or distribution of this can be primarily one mineral or material, or it can be a document and credit is given to the DEQ GSD and the author(s). This copyright statement must appear in any and all electronic mixture. However, in the most general sense sand is or print documents using this file or any part thereof. considered any loose, granular material having grains which are sand sized. Technically, sand is restricted to particles ranging from 0.0625 to 2.0 millimeters in Table of Contents diameter. That is a vast range of sizes. Many people have tried to define sand more precisely. It should be kept in mind that characteristics of sand may vary INTRODUCTION....................................................... 2 greatly within a deposit. WHAT IS SAND?...................................................... 2 Additional confusion arises because the term sand is used to describe a deposit or area, regardless of WHAT ARE SAND DUNES?.................................... 2 particle size. To a geologist the term would be HOW ARE SAND DUNES FORMED? ..................... 2 improperly used if 50 percent or more of the grains are not sand size. In summary, it should be pointed out WHERE DO WE FIND SAND DUNES? ................... 4 that there are more than 100 terms which apply to WHY ARE SAND DUNES FOUND IN sand and sandstone (the major rock formed from MICHIGAN? ................................................. 6 sand). DUNE CYCLES......................................................... 7 WHAT ARE SAND DUNES? USES OF DUNE SAND ............................................ 8 Sand dunes are mounds of windblown sand which vary DUNE ENVIRONMENT............................................. 9 greatly in size, from less than one meter to tens of SELECTED BIBLIOGRAPHY................................. 11 meters high. The size depends upon the supply of sand. There is even greater variation in the area OTHER THINGS TO LOOK FOR AT THE DUNES 12 covered by dunes. In Michigan, the smallest dimension is usually the distance from the shore inland. Many of the more recognizable dune forms are INTRODUCTION ridges or complexes of mounds or crescents. The shape of individual dunes is equally variable. Shape More and more, "natural resource" is becoming a relates to the direction and strength of the wind forming household word. Increasingly, we have become aware it, as well as to the amount of sand available. of the importance of our natural resources and some of the problems relating to wise resource development, management and use. A major point to remember is HOW ARE SAND DUNES FORMED? that some resources are non-renewable. That is, they cannot be replaced, replanted or regrown. In Sand dunes can and do form in many areas. However, Michigan, one non-renewable resource is commonly some requirements must be met. Required elements overlooked - or even taken for granted. The resource are: I) a source of dry sand, 2) a means to sort and is sand. In particular, sand dune sand. Sand dunes transport the sand, and 3) a land area on which to are a natural wonder with beauty and majesty all their deposit the sand. Recent studies indicate that a supply own. However, when you know more about the dunes, of dry sand is the most important factor. The means of they take on even greater significance. Once you learn transporting and sorting are not rare or out of the about the complex, dynamic dune ecosystem, you will ordinary. Running water and normal winds can do this. appreciate dunes even more. Because of the high Strong winds or water action cannot initiate dune demand for Michigan dune sand and its unique formation without a supply of sand. As mentioned, the size and shape of a dune depend on the wind and MI DEQ GSD - Michigan’s Sand Dunes - PA 07.PDF page 2 of 12 amount of sand available. The amount of sand being equal, wind conditions have a strong influence on the shape of a dune field. Constant winds tend to form more regularly shaped dunes or even long ridges. Irregular or changing wind directions result in irregular- shaped dunes. The sand making up Michigan's dunes is almost all one mineral - quartz. However, there are dunes elsewhere in the world which are made primarily of other minerals, such as calcite or gypsum. Because sand dunes are wind-laid deposits, they are formed in layers (stratified). Furthermore, the general shape of a En echelon and overlapping dunes Idealized parabolic dune Domal dunes Dune platform Association of various dune forms dune results in two different sets of beds. There is a gently sloping windward set of beds and a more steeply sloping downwind set. At times, the dunes move or migrate. This movement results in cross- bedding of the sand layers. The cross-bedding found in sand dunes helps geologists to distinguish dune deposits from other landforms. Because quartz grains can form from a number of different rocks, the original source of the quartz dune sand cannot be singled out. It should be noted that relatively few bedrock outcrops occur in Michigan. Instead, glacial drift almost completely covers the State. Therefore, one can safely assume that sand for Overriding dunes the dunes comes from the drift. Yet, much of the sand found in drift is mixed with a variety of other particles, MI DEQ GSD - Michigan’s Sand Dunes - PA 07.PDF page 3 of 12 from clay to cobble size. The drift is eroded, transported, sorted and redeposited by water - the running water of a river or the pounding surf of a beach. Water tends to concentrate sand-sized particles in particular areas. Continued erosion and transportation of sand replenishes the sand blown into the dune. As long as WHERE DO WE FIND SAND DUNES? more sand is supplied, the dunes will continue to grow. In Michigan, sand dunes are found along much of the When the supply diminishes, the dunes are likely to shoreline of the Great Lakes. The best known and stabilize, or at least stop growing. Places where sand most studied Michigan sand dune areas are along accumulates are numerous in near-shore Lake Michigan. Here, the supply of dry sorted sand environments. You may have noticed this along many and a prevailing wind direction toward land lead to of the lovely beaches. Sand, if available, accumulates dune development. However, close inspection shows on the beach as well as out into the lake to a varying that some of the dunes or dune-like structures are not degree. close to today's lake shoreline. These inland dunes The size range of sand grains that make up dunes is reflect previous dune-forming conditions. These dunes remarkably close. This is because grains that are are a result of massive ice sheets which covered smaller-than-sand-size (silt or clays) are carried farther Michigan, and much of North America, during what away by the action of wind and water. Grains or geologists call the Pleistocene Epoch, some 1,800,000 stones that are larger-than-sand-size (pebbles, years ago. Glaciers transported sand and other cobbles, boulders, and the like) are left behind. When materials and deposited them as glacial drift. Large enough of the larger materials (usually small to masses of glacial ice gouged out the basins that now confused with tubes formed around the roots of plants confine the Great Lakes. growing on the dunes. An easy test will distinguish a However, the glaciers did not simply advance and fulgerite from a root cast. Place the specimen in a retreat. Instead, a complex sequence of advances and container of vinegar. If it fizzes and falls apart, it was a retreats occurred. These fluctuations had great impact root cast. The cementing material was dissolved by on the landforms. At times drift was deposited, forming the slightly acid vinegar. However, if the specimen is a barriers which ponded meltwaters in large lakes. fulgerite, it will not be affected to any great extent by When the barriers were eroded or otherwise breached, the vinegar bath. lake levels changed. When the water level dropped, medium size stones, 10 mm or more) are left behind, a sand deposits could dry out and then be blown into rock pavement or lag gravel is formed.